Whole-genome resequencing to evaluate life history variation in anadromous migration of Oncorhynchus mykiss

Pacific salmon and trout experience physiological modifications necessary to migrate between vastly different freshwater and marine environments. Some species such as the protected Oncorhynchus mykiss, demonstrate variation in life history strategies with some individuals remaining exclusively in freshwater, known as rainbow trout, while others undergo migration to the ocean and return to freshwater to spawn, known as steelhead. Since there is limited understanding of genes involved in this life history variation, we evaluated the genomic difference between known migrating steelhead and freshwater rainbow trout. Sequencing of these collections yielded 5.64 million positions in the genome that were tested for significant differences between steelhead and rainbow trout groups along with previously identified candidate gene regions. While a few regions of the genome were marginally significant, there was one region that provided the most consistent signal of association with migration. Previously identified candidate genes for migration in coastal steelhead and rainbow trout were not informative for this population. Results indicate that the significant region may represent a minor effect gene for male migration and suggests that this life history variation in Oncorhynchus mykiss is more strongly driven by other mechanisms related to environmental rearing.